At present, the most common forms of automotive internal combustion engines for use in passenger cars and the like utilize cylinder block and crankcase castings of iron or aluminum as main portions of the engine frame. This frame usually carries one or more cylinder heads and an oil pan, the latter enclosing a forged or cast crankshaft connected by cast or forged connecting rods to pistons in the cylinders. A camshaft and valve gear actuate valves in the cylinder head while various accessories for the engine and vehicle are mounted externally on the engine frame and driven by V-belts or other means.
Other forms of construction have also been used commercially, including fabricated sheet metal frames, but problems of cost and durability have apparently been responsible for a lack of extensive use of such designs.